Non-singing amplifier



Nov. 17, 1931.

G. H. STEVENSON NONSINGING AMPLIFIERA Filed NOV. 10. 1928 Patented Nov.U17, 1931 iid *usarse Artur israel esonera rr. srnvENsoN, or soUNnfBEACH. ocNNncrIcufr, 'essieNoi-t Toni-imams. n

PHONE neneruercnrns, INCORPORATED, or New Yoeri, N. Y., vAV oonronATroNor NEW YORK NON-SING-VANG MPLIFEER Appncationinea November 1o, i928.serial No. 318,354.

rlhis invention relates to high frequency vacuum tube ampliiers and moreparticularly to improved circuits whereby the operating elilciency ofsuch ampliiiers is increased.

A. general ob]- ect of the invention is to prevent undesirable singingor regeneration in high frequency amplifier circuits.

T he prevention of singing due to the interelectrode capacity requiresthat the retro-active E. M. F. (or feed back) at all times be Zero orelse inV such phase relation with respect to the input E. M. as toproduce loss.

of amplilication (or degeneration). Y In accordance with the presentinvention this I1s accomplished by maintaining constant similarvity otthe impedances between the plateiand grid and between the filament andgrid. rlhis produces a degenerative action at all frequencies and alsomakes the degenerative action substantially constant at allJfrequencies.

Two simple tuned circuits are employed which by virtue of mechanicalcoupling of the tuning elements are always resonant at the samefrequency, one circuit beingconnected between the grid and filament andthe other between the grid and plate. By this means, the impedances ofthe two paths are maintained similar at all frequencies and a constantdegenerative feed back is secured. By incorporating the plate to gridbranch as part of the input circuit along with the gridfllament branch,two input E. M. Ffs are introduced, which by the proper poling yof thecircuits, may be made additive with respect to the normal amplifying`action of the tube, and may be made to substantially neutralize eachother with respect to the direct transmission of currents to the outputcircuit through the impedances ot' the tube. The input circuit may forexample be coupled inductively` to both the circuit between gridV andlilament and the circuit between grid and plate. Preferably then thecouplings kwill be reversed with respect to each otherl in phase andbalanced in degree so that no current is directly transmitted to thespace path or the output circuit. input voltages aid in producingamplification.

Both resonant circuits may be tuned by In this case the two' means of aVvariable condenser, in which case it is desirable that their rotors beat `A() ground potential to avoid the disturbances due to handcapacities, and to simplify their mechanical connector. This may be doneby supplying the lilament current through parallel inductive windingsand arranging these windings so that they will comprise a part of thetuning circuit between grid and filanient; supplying the plate potentialthrough the inductivel winding connected between the gridV and plate;and grounding the grid of the vacuum tube. A blockingcondenser isemployed between theplate and output wind-- ing to prevent the platepotential'from being lmpressedonthe lil'ament ot thevacuum tube. Theinvention will be better understood by referring to the followingdescription and accompanying drawings Y showing preferred formsotembodiment. e

Fig. 1 represents a radio receiving circuit comprising two stages ofradio frequency amplilication, a detector, an audio amplifier and a loudspeaker. v l Fig.l l-A is a modified form of that portion of Fig. 1between lines X-X and YV-Y. Referring to Fig. 1 the amplifier tube 1 hasan input circuit between grid 2 and lilament 3 which consists of a coilLl' across which is connected a tuning capacity 5, and an input circuitbetween grid 2 and'plate G'which consists of a coil 7 across which isconnecteda tuning capacity 8. Coil 4 has a biilar winding, one end; otthe bililar windingsbei'ng connected-to the'terminals of the lament 3 ofvacuum tube 1 and the other end connected .across the filament battery9. The antenna a locking condenser to prevent positive ECE i "Bpotential 13 from reaching the filament 3.

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Tuning condensers 5 and S are preferably connectedv to the same controlso that both resonant circuits Ll-- and 7 8 may be tuned together.Preferably also, the rotors 17 and 18 of condensers 5 and 8 areconnected to grid 2. This arrangement permits grounding the grid 2 ofthermionic tube 1 as shown at 19. YThe effect of hand capacities'oncondensers 3 and 5 is thereby reduced-to` a minimum. Y

Since both resonant circuits are tuned at the same ti1ne,no ysingingtakes place even when the circuits are beingv tuned to the desiredfrequency because of the fact that the similarity of the impedances ofthe two circuits 4 5 and 7 8. maintains lthe grid 2 constantly at anoscillating potential midway between the plate 6 and the .filament 3.Furthermore, by maintaining` constant the similarity of the impedancesbetween plate 6 and grid 2 and between the lgrid 2 andthe filament 3 adegenerating action takes place which is substantially constant at allVfrequencies. rlhe amount of degeneration can be controlled byv varyingthe values Vof the impedances of circuits land 7 8. As the impedance ofcircuit 7 8 is increased over that of circuit 4 5, the amount ofdegeneration decreases. The impedances will be in the ratio of theinductances of the tuning coils when appropriate tuning condensers areused.

The coupling from the antenna circuit to the input circuit of vacuumtube 1 through coils 11 and 12 is reversed with respect to the inputcircuits and balanced so that no current flows from plate 6 and grid 2.The input voltages to coils 4 and 7 then aid in producing amplification.

The second stage of hiO'h frequency amplification comprises an amplifiertube 21 having an input circuit similar to that of amplilier tube 1 andcomprising aninputpcoil 24 lconnected between `grid 22 and filament 23,

and anpinput coil 27 connected between grid 22 and plate 26. Coils 24and 27 Vare inductively coupled. Variable condensers 25 and 28 areconnected across coils 24 and 2'?, respectively, for tuning' purposes.As-indicated by the dotted lines, they are preferably tuned at the sametime in a manner similar to condensers 5 and 8.

Anl additional circuit 20 30 comprising an inductance coil 20 and animpedance 30 is inductively coupled to coil 27. Coils 16 and 2O are soconstructed to have similar characteristics. The value of the impedance30 is preferablymade the same as the plate filament impedance of vacuumtube 1. This circuit 20 30 then simulates the effect of the circuit15e-16 which is inductively coupled to circuit 24 25. Circuit 20 30 willin `general be unnecessary7 wnen coils 16 and 24.- are loosely coupled.In this case only one input, E. M. F. is present, and a certain directtransmission may talre place between the input and the output circuitsof the tube. rlhe non-oscillating qualities of the circuit are howevernot affected.

The output circuit of Vacuum tube 21 is coupled through coil 36 to adetector circuit so that the signalingwaves p ss to the detector andfrom the letect r through the audio amplifier to the loud speaker. lfstill greater amplification of the high frequency signals is desired anadditional stage or stages similar to the two shown, can be added.

The modified interstage radio frequenc)Y coupling arrangement of Fig.com- .prises two inductances 31 and 32 connected in the output`circuit-*of thermionic tube 1 having their couplings reversed withrespect to each other. Inductance 31 is inductively coupled toinductance 27 and inductancc is ind ctively coupled to inductance ylieinput voltages to coils and 2'? then aid in producing amplification.

`The circuit Cif-Fig. 1 has been illu. 'lrated and described :isemploying different circuit connections in the two radio frequency stagIt will be understood, of course, that this is .iter purposes ofillustration and that it 1s within the invention to employ eitheridentical or different types of circuits in the different stages. Forexample7 to use the same type of connection for stage 2 that is used forstage 1 it is merely necesi-:ary to replace the elements includedbetween the lines K X. and Y Y of Fig. 1 by the elements shown in Fig. 1A.

While several embodiments of the invention have been shown and describedin detail, it is understood that the invention is generic in characterand is not to be construed as limited to these particular embodimentssince numerous modifications thereof may be made by ersons skilled inthe art without departing' from the spirit of applicants invention, thescope of which is to bc determined by the appended claims.

, That is claimed is:

1. The combination of an evacuate Vessel having a plurality ofelectrodes incl ding grid, a. plate and a filament, a source of esci,-lations of an ultra-audio frequency, and means coupled to said source ofoscillations for maintaining` the grid constantly at an oscillating`potential intermediate betwee the plate and the filament, said meansceniprising two circuits resonant at the same frequency, one connectedbetween grid and plate and the other between grid and filament.

2. In an electrical system comprising a thermionic device having acontrol electrod an anode.I and a cathode7 means for ground-- ing saidcontrol electrode. an input circuit. an output circuit including theanode and cathnseaaen controlelectrode ands'aid cathode, anntlier partof said input circuit including said control electrode andY said anode.

3...-Radio, frequency amplifying apparatus comprising a thermionicvacuum tube having a lamen't, grid and plate, two equal inductances,apair ofv simultaneous adjustable condensers of equa-l capacityconnecte-d lin eec.- tive shunt to said inductances, and adapted to tunesaid inductances, ,to resonance with a signa-l, ineans associated with'said condensers whereby the adjust-nient. of one, accompanied by theadjustment of the other, leads from said filament to one end ofone ofsaid inductances, a. lead froinsaid'plate. to one end of the other ofsaid inductances, a connection from said grid tothe other ends of saidinductances, said connection to one of said inductances including acapacity, and an inductance and a capacityin the output circuit of saidtube. v

et. Radio. frequency amplifying apparatu comprising a tliermioni'cVacuum tube having a filament, grid and plate, two equal inductances,one of said inductances comprising two conductors bililar wound tovpermit the filament to have one D. C. potential and a different A.. C.potential with respect to the other electrodes, a pairof simultaneousadjustable condensers of equalcapacity con-'` nected in effective shuntto said inductances and adapted to tune said inductances to resonancewith a signal, inea'ns associated with said condensers whereby theadjustment of one is accompanied by the adjustment of the other, leadsfrom said filament' to said biiiiar. wound inductance, a lead from saidplate to one end of the other of said inductances, a connection fromsaid grid to the other end of Ysaid inductance connectedfto said plateand a connection from said grid to one of the two conductors of saidbiiilar wound 'inductance, said connectionto said inductance connectedto said plate including a capacity, and an inductance and acapacity 1 inthe output circuit of said tube.V

5. Radio frequency amplifying apparatus comprising a thermionic Vacuumtube having a filament, grid and plate, an inductance, a variablecapacity connected in effective shunt to said inductance and adapted totune said inductance to resonance Ywith a signal, a lead from saidplate'to one end of said inducta-nce, a connection from said grid to theother end of said inductance, said connection including a capacity, asecond in@ ductance comprising two conductors bifilar and an.indructanceand` acapacity in the. output circuit ofsaid tube.V

' 6. Aradioreceiving circuitcomprising an antenna circuit, a .pluralitylof three-element radio frequency amplierl tubes having a grid, a plateand a lilament andy connected' in cascade', each of said; radiofrequency anrplilier tubes having associated therewith an inductanceyavariable capacityV connected in effective shunt to said inductance, andadaptj ed to tune said inductance to resonance with' a signal, a leadfrom said plate to one end of said inductance, a connection from saidgrid vtno-theother-'end of said rinductance, said connection includingya capacity, a second 1nrducta-nce comprising two conductors bifilarwound, a rrariable capacit,7 connected in ef- :fective shuntto one ofsaid; bililar windings,

and` adapted to tune said inductance to resonance with said signal, aconnection from one end of said last. mentioned bilar windingto saidarida connections' from the other ends of said bifilar windings to `saidfilament` and an inductance and a capacityv in the output circuitadetectorl circuit coupled to the outa c ,sr-rid and plate, andthe otherof said antenna inductances` coupled to said inductance con-` nectedbetween grid and filament.

7.Radio frequency amplifying apparatus comprising a thermionicvacuuintube having a filament, arid and plate. an inductance, a variablecapacity connected in effective shunt to said -inductance and adapted totune said i mentioned bililar winding-to said grid. connections from theother ends of said bifilar windinns to said filament, an inductance and120 a capacity in the output circuit of said tube,

an input circuit inductively coupled to said bifilar wound inductanceanda circuit comprisingan inductance and an eliectiae resistance,simulatingy the inductance and eiiective l resistance of 4said Vinput,circuit, inductively coupled to said inductance connected between saidgrid and' plate.`

8. Aradio receiving` circuit comprising an Y antennay circuit, aiplurality of'threeeelement 3U radio 'frequency amplifier tubes having agrid, a plate and a filament and connected in cascade, each of saidradio frequency amplifier tubes having associated therewith aninductance, a variable 'capacity connected in effective shunt to saidinductance, and adapted to tune rsaid inductance to resonance with asignal, a lead from said *plate to one end of said iiiductance, aconnection vfrom said grid to the other end of said inductance, saidconnection including a capacity, a second inductance comprising twoconductors bifilar wound, a variable capacity connected in effectiveshunt to one of said biiilar windings, and adapted to tune saidindiictance to resonance with said signal, a connection from one end oflsaid last mentioned bifilar winding' to said gri d, connections from theother'ends.

of said biiilar windings to said filaineiit,"and an inductance and acapacity in the output circuit, each of s'aid'radio frequency-amplivtier tubes, with the exception of the tube connected to saidantenna circuit, having a circuit comprisingV an inductance and aneifective resistance which simulates the inductance and effectiveresistance of the output circuit of the preceding' amplifier tubeinductively coupled to said induc'tance connected between said @rid andplate; a detector circuit, an audio amplifying circuit and a soundreproducing device, said antenna circuit including two inductanceshaving their couplings reversed with respect to each other, one of saidinductances'inductivelv coupled to said inductance lconnected betweengrid and plate, and the other of said antenna inductances coupled tosaid inductance connected between grid and filament.

9. Ina radio system of communication the combination with athree-electrode thermionic tube. having an input circuit and an outputcircuit of an input transformer having two secondarics inY said inputcircuit, one of said secondaries connected between the control electrodeand anode of said thermionic tube and the other of said secondariesconnected between said control electrode and the 'cathode of saidthermionic tube. said secondary windings of said input tran sforineroperating to maintain said control electrode constantly at anoscillatina potential intermediate between said anode and cathode,an'output transformer havingl a primarv in said output circuit', and

plate of the following radio frequency ainplitler Vtube and the otherinductively coupled to saidr inductance connected between the grid andfilament of said last mentioned tube.

ll. The combination with an evacuated i vessel having a Vplurality ofelectrodes, of a` aiidion having a grid, an anode and a cathode y andhaving capacity between the grid and the anode and having a timed inputcircuit be tween said grid and said cathode, means for preventingregeneration due to said gridanode capacity comprising a tuned circuitconnected between grid and anode and tuned syntonously with said timedinput circuit.

13. The combination with a vacuum tube 'having a plurality of electrodesbetween two of which electrodes there is a capacity tend ingito produceregeneration, of a source of oscillations of a certain frequency, andmeans comprising a circuit resonant to said certain frequency connectedbetween said two electrodes and coupled to said source of oscillationsfor neutralizing the regenerative capacity eect between said twoelectrodes for said certain frequency.

M. The combination defined in claim 9, including also a wave source, andmeans for coupling said wave source to each of said tuned circuits.

15. The 'combination defined in claim 9, including also an incomingcircuit coupled to the inductances of each of said timed circuits andpoled with respect thereto to produce excitation therein 'in opposingphases.v

In witness whereof, I hereunto subscribe GEORGE sTEvENsoN.

